1. Field of the Invention
The present invention relates to nanowires, and more particularly, to nanowire harvesting and reducing or removing contamination in nanowires.
2. Background of the Invention
Nanomaterials, and in particular, nanowires have the potential to facilitate a whole new generation of electronic devices. For example, In certain cases, uses of nanomaterials have been proposed that exploit the unique and interesting properties of these materials more as a bulk material than as individual elements requiring individual assembly. For example, Duan et al., Nature 425:274-278 (September 2003), describes a nanowire based transistor for use in large area electronic substrates, such as, displays, antennas, and the like that employ a bulk processed, oriented semiconductor nanowire film or layer in place of a rigid semiconductor wafer. The result is an electronic substrate that performs on par with a single crystal wafer substrate that can be manufactured using conventional and less expensive processes than those used to manufacture poorer performing amorphous semiconductors, which is also more amenable to varied architectures, such as, flexible and/or shaped materials.
In another example, bulk processed nanocrystals have been described for use as a flexible and efficient active layer for photoelectric devices. In particular, the ability to provide a quantum confined semiconductor crystal in a hole conducting matrix (to provide a type-II bandgap offset), allows the production of a photoactive layer that can be exploited either as a photovoltaic device or photoelectric detector. When disposed in an active composite, these nanomaterials are simply processed using standard film coating processes. See, e.g., U.S. Pat. No. 6,878,871, which is incorporated herein by reference in its entirety.
In accordance with these uses of nanowires and other nanomaterials, the new process requirement is the ability to provide a film of nanowires that are substantially oriented along a given axis. The technology for such orientation has already been described in detail in, for example, U.S. Pat. Nos. 6,962,823, 7,051,945, and 7,067,328, and International Publication No. WO 03/085701, which all are incorporated herein by reference in their entirety.
A major impediment to the emergence of this new generation of electronic devices based on nanostructures is the ability to effectively grow nanowires and other nanostructures that have consistent characteristics and that are free of catalysts and contaminants. Current approaches to harvest and integrate nanowires do not facilitate mass production, do not yield consistent nanowire performance characteristics and can be improved to generate better device performance based on nanowires. For example, nanowires grown using a vapor-liquid-solid process are often subject to contamination from the initiation catalyst that may be left behind within and/or at the tip of a nanowire. Such catalysts often have adverse effects on the conductive and other properties of the nanowires. In addition, nanowires may also contain various contaminants or growths near the initiation point of the nanowire, which can also have deleterious effects on nanowire performance.
What are needed are systems and methods for nanowire harvesting and integration that facilitate mass production, yield consistent nanowire performance characteristics and generate improved device performance.